The three videos use the band model to illustrate how charge carriers move in semiconductors.
The first video shows undoped semiconductor material. The conduction band is visible at the top and the valence band at the bottom. A single electron is excited and moves into the conduction band. Due to an externally applied electric field, the electron moves toward the positive terminal.
The position where the electron was located is now unoccupied (marked by a red circle). The neighboring atom fills this hole, leaving behind a hole of its own. This process repeats. This conduction mechanism in the valence band is called hole conduction.
Note: The video was produced in HD quality. The quality has been significantly reduced in the YouTube player. You can download the video in high resolution below. To play the video here in reasonable quality, select “HD 1080p” in the YouTube player settings.
The second and third videos show conduction processes in doped semiconductors (solar cells). A PN junction forms inside, which distorts the energy bands. At this junction, the so-called space charge region (SCR) is created. This is an area with an electric field.
Charge carriers in semiconductors move in two ways: by diffusion (random movement due to temperature) and by drift (directed movement in an electric field). In the SCR, drift dominates over diffusion. As a result, holes migrate to the P-region and electrons to the N-region.
Whether a charge carrier reaches the contacts of the solar cell depends on its lifetime and diffusion length. If it reaches the contacts in time, a usable voltage is generated there.
The band model shows how light energy is converted. Light lifts electrons into the conduction band, where they possess higher kinetic energy. When transitioning to the other layer, this energy is released and stored as electrical energy at the contacts.
Related Animations
Web Animations
Overview and Download
| Title | Conduction Processes in Semiconductors |
| Target Audience | Teachers and lecturers (Level: upper secondary, university) |
| Features | Fullscreen mode lossless zoom large screens and projectors supported |
| License | Freeware (for non-commercial use) |
| Download | Download Videos |
Contributors
C. Hein, S. Rikowski